The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, US patent applications identified by their US patent application serial numbers (USSN) are listed alongside the Australian applications from which the US patent applications claim the right of priority.
Not applicable.
The present invention relates to fluid dispensing. In particular, this invention discloses a fluid-dispensing chip.
This invention is a development of a printing technology that has been developed by the Applicant. This development can be traced by considering the referenced patents/patent applications set out above.
Many different types of printing have been invented, a large number of which are presently in use. The known forms of printing have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques of ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different types. The utilisation of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electro-static field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et al. in U.S. Pat. No. 3,946,398 (1970) which utilises a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezo-electric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a Piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a sheer mode type of piezoelectric transducer element.
Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclosed ink jet printing techniques rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Manufacturers such as Canon and Hewlett Packard manufacture printing devices utilising the electro-thermal actuator.
As can be seen in the above referenced matters, Applicant has developed an ink jet printing technology that uses micro-electromechanical components to achieve the ejection of ink. The use of micro-electromechanical components allows printhead chips to have a large number of densely packed nozzle arrangements without the problems associated with heat build-up.
Applicant envisages that this technology can be used to dispense fluid. This invention is therefore intended to be a simple development of the technology that has already been the subject of many patent applications filed by the Applicant.
According to the invention, there is provided a fluid-dispensing chip that comprises
a wafer substrate that incorporates drive circuitry, and
a nozzle assembly positioned on the wafer substrate, the nozzle assembly comprising
nozzle chamber walls and a roof wall that define a nozzle chamber and a fluid ejection port in the roof wall, and
an electrostatic actuator that comprises
a first planar electrode positioned on the wafer substrate, and
a second planar electrode that is positioned in the nozzle chamber and is displaceable towards and away from the first planar electrode to eject fluid from the fluid ejection port, the first planar electrode and the second planar electrode being connected to the drive circuitry so that a potential difference can be applied between the planar electrodes to displace the second planar electrode towards and away from the first planar electrode,
at least one of the nozzle chamber walls and the wafer substrate defining a fluid inlet in fluid communication with the nozzle chamber and a fluid supply source, said first planar electrode and said second planar electrode defining an air gap between the first and second planar electrodes.
At least one of the nozzle chamber walls and the substrate may define an air path in fluid communication with an external atmosphere so that air flows into and out of the air gap when the second planar electrode is displaced towards and away from the first planar electrode.
The electrodes may have facing surfaces that are coated with a material having a low coefficient of friction to reduce possibilities of stiction. Said material may comprise substantially polytetrafluoroethylene.
Instead, or in addition, one of the first and second planar electrodes may have at least one projection that extends towards the other electrode to ensure that the electrodes do not touch when the second planar electrode is displaced towards the first planar electrode.
Said second planar electrode may include a layer of stiffening material for maintaining a stiffness of the second planar electrode. The stiffening material may be silicon nitride.
The roof wall may define a plurality of etchant holes to facilitate etching of sacrificial layers during construction.